1. Field of the invention
This invention relates to a transparent, fire-resistant, glazing panel comprising at least one layer of intumescent material bonded to at least one structural ply of the panel. The invention extends to a method of manufacturing a transparent fire-resistant glazing panel comprising forming a sandwich assembly from a plurality of vitreous plies with successive vitreous plies in contact with an intervening layer of intumescent material and subjecting that sandwich to heat and pressure conditions such as to degas the inter-ply spaces of the sandwich and to cause the sandwich assembly to be bonded together as a transparent laminate.
2. Description of the Related Art
Layers of intumescent material are often associated with sheets of glazing material to form transparent, fire-resistant panels. For example such a layer may be sandwiched between two glass sheets. Very important uses of such panels are as screens which permit illumination of a screened area and as closures of viewing apertures of rooms or other enclosures where there may be a risk of fire.
Hydrated metal salts, for example metal silicates, especially alkali metal silicates have been used as intumescent materials in such panels for some years. On the outbreak of fire, the water of hydration is driven off by the heat of the fire, and the layer of intumescent material becomes converted to an opaque foam which serves as a barrier to both radiated and conducted heat.
It is also known that that layer may serve to bond together structural sheets of the panel such as sheets of glass which may become shattered by thermal shock due to the fire. The effectiveness of the panel as a barrier against the passage of fumes and flames is thus also prolonged to some extent, but it is soon destroyed after the last glass sheet of the panel breaks.
Typically, the effectiveness of such panels is tested by mounting them in a wall of a furnace whose interior temperature is then increased according to a pre-determined schedule.
Details of such a test are specified in International Standard No ISO 834-1975. The fire-resistance test procedure set out in that Standard is also referred to in International Standard ISO 9051-1990 which speaks specifically of the fire-resistance characteristics of glazed assemblies. It is appropriate to quote some passages from that latter Standard here.
"Glass is a non-combustible material and therefore will not contribute to or propagate fire. PA1 "Glass if affected by heat may fracture by thermal shock or may soften and then not be held by the frame. Only certain types of glazed assemblies are, therefore, recognised as fire-resisting. The ability of glazed assemblies to resist fire depends on the type of glazed products, glazing method, frame type, pane size, fixing method and the type of construction surrounding the glazed area. PA1 "Some transparent and translucent glazed assemblies can meet requirements for stability and integrity (RE), and in some cases insulation (REI, where R is for resistance, E for etancheite and I for insulation). PA1 "Not only is the possibility of direct fire propagation through openings caused by glass breakage to be considered for fire protection precautions: it may also be necessary to take into account the heat transmitted through the glazed assembly, which may still be intact, as such heat may cause ignition of combustible materials. PA1 "Glazed assemblies of fire-resistance according to class RE under the fire conditions as defined in ISO 834 provide, for a given time, stability and integrity. The temperature of the unexposed side is not taken into account. PA1 "Glazed assemblies of fire-resistance according to class REI under the fire conditions as defined in ISO 834 provide, for a given time, stability, integrity and insulation." PA1 R.sub.ti the difference in height between the top of the highest peak and the bottom of the deepest valley in any given sampling length i. It may be noted that this is equivalent to R.sub.y as defined in ISO 4287. PA1 R.sub.tm the mean of all values of R.sub.ti measured over the whole assessment length. It may be noted that this is equivalent to R.sub.z DIN as defined in DIN 4768.
There are different grades of fire-screening panel, and among those commonly recognised are grades which correspond to panels which are effective against flames and fumes for periods of 15, 30, 45, 60, 90 and 120 minutes.
The insulation properties which a panel must afford in order to meet the standard to REI level are, briefly, that no point of the surface which is exposed to the exterior of the furnace may undergo an increase in temperature of more than 180.degree. C. above its initial (ambient) temperature, and the mean temperature increase of that face must not exceed 140.degree. C. Such panels belonging to class REI may also form barriers against the transmission of infra-red radiation from the seat of a fire.
When a panel incorporating an intumescent layer sandwiched between two sheets of glazing material is exposed to the outbreak of a fire, the intumescent material will be broken down and will expand into a mousse or foam. The glazing material may be softened under the heat evolved by the fire, or it may fracture due to thermal shock. It will be appreciated that the sheet of glazing material closest to the fire will be at greatest risk of fracture due to thermal shock, and accordingly various proposals have been made to reduce the tendency of that, or some other sheet, to fracture.
For example British Patent Specification No 2 096 944 proposes to make use of a sheet of a boro-silicate or other special vitreous material having a low coefficient of thermal expansion thus reducing the degree of thermal shock for a given temperature gradient in the sheet. It has also been proposed to make use of tempered glass which is in theory better able to withstand thermal shock. Increasing the thermal shock resistance of one or more of the sheets of the panel in either of those ways, especially if rather thick sheets are used, will afford some increase in fire-resistance. However, this will also add to the costs of manufacturing the panel, and it may also add to its weight.
If a sheet of the panel, for example the sheet closest to the fire, should become fractured, the foamed intumescent material will tend to displace the resulting fragments. While the foamed intumescent material tends to cling to any such fragments retaining them in position, this tendency is reduced as temperature is increased, and a displaced fragment may slide down the window tending to shear the foamed layer, dragging much of that foam with it and thus exposing the next structural ply of the panel to the full force of the fire. And so destruction of the integrity of the panel proceeds.
Clearly, the panel must maintain some sort of structural integrity if it is to remain effective as a barrier to flames, fumes and direct heat radiation. For that reason the practice has been adopted of increasing the number of layers of intumescent material and the number of the sheets of glazing material, of using thicker layers of intumescent material, and also of increasing the thicknesses of the glazing sheets in order that fragments may not be so easily displaced to fall.
Any such increase in the mass per unit area of the panel will give rise to certain additional costs, not only in materials, but also in storage, handling and transport. It will also result in the need for a significantly more robust and thus more expensive frame for installation in the structure where it is required. Increasing the thickness of a layer of intumescent material makes it more difficult to achieve a high degree of transparency.